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Air pollution linked to increased risk of anxiety and stroke
New series of articles examine the association between air pollution and health
Air pollution is linked to a higher risk of stroke, particularly in developing countries, finds a study
published in The BMJ today. In a second article, new research also shows that air pollution is
associated with anxiety.
Stroke is a leading cause of death and kills around 5 million people each year worldwide. Common
risk factors include obesity, smoking and high blood pressure. But the effect of the environment,
such as, air pollution is uncertain because evidence is lacking.
In a systematic review and meta analysis, a team of researchers from Edinburgh University looked at
the association between short term air pollution exposure and stroke related hospital admissions
and deaths. In total, they analysed 103 observational studies that covered 28 countries across the
world.
Gaseous pollutants included in the analysis were carbon monoxide, sulphur dioxide, nitrogen dioxide
and ozone. In addition, particulate matter was included: PM 2.5 (fine particles less than 2.5 µm in
size) and PM 10 (coarse particles less than 10 µm in size).
Results showed an association between carbon monoxide (1.5% increased risk per 1 ppm), sulphur
dioxide (1.9% per 10 ppb) and nitrogen dioxide (1.4% per 10 ppb) and stroke related hospital
admissions or death. The weakest association was found for ozone.
Both PM 2.5 and PM 10 were associated with hospital admissions or deaths due to stroke, by 1.1%
and 0.3% per 10 µg/m3 increment respectively. The first day of air pollution exposure was found to
have the strongest association.
Low- to middle-income countries experienced the strongest associations compared to high-income
countries. Only 20% of analysed studies were from low- to middle-income countries - mostly
mainland China - despite these countries having the highest burden of stroke.
Higher concentrations of gaseous pollutants were measured in middle- to low- income countries
when compared to high-income countries. These results suggest a need for policy changes to reduce
exposure in such highly polluted regions, conclude the authors.
Previous research has shown that air pollution can affect the cells that line the circulatory system
and increase activity of the sympathetic nervous system, which can lead to narrow blood vessels, an
increase in blood pressure, the restriction blood supply to tissues and increase the risk of
thrombosis.
A second study from researchers at The Johns Hopkins and Harvard Universities examined the
association between particulate air pollution and anxiety.
Anxiety is the most common psychiatric disorder and globally affects around 16% of people at some
point in life. It is associated with lessened productivity, increased medical care and risk of suicide.
Overall, 71, 271 women, aged between 57 and 85 years, were included in the analysis. Data were
taken from the US Nurses’ Health Study.
Exposure to particulate matter, PM 2.5 and PM 2.5-10 was determined from national geographic
and meteorological data, and estimated from five periods (one month, three months, six months,
one year and 15 years) before assessment of anxiety.
Distance from residence address to the nearest major road, a common indicator for traffic related
air pollution exposure, was also analysed.
An anxiety questionnaire that included eight self-rated questions on symptoms including fearfulness,
desire for avoidance and tendency to worry was completed by each participant.
Factors including socioeconomic status, education, age and marital status were all accounted for.
Findings showed that around 15% of women experienced high anxiety symptoms. Exposure to
particulate matter was linked to a higher risk of anxiety. While PM2.5 was found to have a significant
association with anxiety, no such link existed with PM 2.5 - 10.
Women who resided 50 to 200m from a major road were more likely to have higher anxiety
symptoms than those living more than 200m away. But those living within 50m of a major road did
not experience this association.
Recent exposure, on the other hand, was found to have a more significant association with anxiety efffects were strongest following the first month of exposure.
Particulate matter air pollution may trigger or worsen anxiety through oxidative stress and
inflammation or deteriorate an existing health condition, explain the authors.
Both studies were observational and no definitive conclusions can be drawn about cause and effect,
and the teams of researchers call for more research.
In an accompanying editorial, Michael Brauer from the University of British Columbia, Canada, writes
that these studies “confirm the urgent need to manage air pollution globally as a cause of ill health”
and that reducing “air pollution could be a cost effective way to reduce the large burden of disease
from both stroke and poor mental health.”
[Ends]
Note to Editors:
Research article: Short term exposure to air pollution and stroke: a systematic review and meta
analysis
Journal: The BMJ
Embargo link to research: http://press.psprings.co.uk/bmj/march/airpollstroke.pdf
Public link after embargo lifts: http://www.bmj.com/cgi/doi/10.1136/bmj.h1295
Research article: The relation between exposure to fine particulate air pollution and anxiety: a
cohort study
Journal: The BMJ
Embargo link to research: http://press.psprings.co.uk/bmj/march/airpollanx.pdf
Public link after embargo lifts: http://www.bmj.com/cgi/doi/10.1136/bmj.h1111
Editorial: Air pollution, stroke and anxiety
Journal: The BMJ
Embargo link to research: http://press.psprings.co.uk/bmj/march/airpolled.pdf
Public link after embargo lifts: http://www.bmj.com/cgi/doi/10.1136/bmj.1510
Contacts:
Research: Anoop Shah, Centre for Cardiovascular Science, University of Edinburgh, Scotland, UK
Email: anoop.shah@ed.ac.uk
Tel: +44 776 654 4156
Research: Melinda Power, John Hopkins Bloomberg School of Public Health, USA
Email: melindacpower@gmail.com
Tel: +1 443 287 6027
Editorial: Michael Brauer, Professor, School of Population and Public Health, University of British
Columbia, Canada
Email: michael.brauer@ubc.ca
Tel: +1 604 822 9585